Process of producing silver-or silver-copper alloy-metal oxide composite material

Abstract

A silver-metal oxide composite material comprising a silver matrix or silver-copper alloy matrix containing 50% by weight or less of copper, (a) from 0.5 to 25% by weight, in terms of elemental metal, of an oxide of at least one element selected from the group consisting of Mg, Al, Zr, Ca, Ce, Be, Th, Sr, Ti, Cr, Hf and Si, and, optionally, (b) from 0.01 to 5% by weight, in terms of elemental metal, of an oxide of at least one element selected from the group consisting of Bi, Pb, Cd, Zn, Sn, Sb, Mn and iron family metals; the oxide of the (a) element and, where present, the oxide of the (b) element being dispersed in the form of fine particles with a particle size of not more than about 0.1 mu m uniformly throughout the matrix from the surface to the core thereof; and process of producing the composite material using oxidation under the conditions in which a liquid phase and a solid phase coexist.

I claim: 
     
       1. A process for producing a silver-metal oxide composite material comprising the steps of: (A) raising the partial pressure of oxygen and heating therein a mixture comprising silver, (a) from 0.5 to 25% by weight, in terms of elemental metal, of at least one element selected from the group consisting of Mg, Al, Zr, Ca, Ce, Be, Th, Sr, Ti, Cr, Hf and Si in a metallic and/or oxide state and, optionally, (b) from 0.01 to 5% by weight, in terms of elemental metal, of at least one element selected from the group consisting of Bi, Pb, Cd, Zn, Sn, Sb, Mn, Fe, Ni and Co, in a metallic and/or oxide state to thereby bring the mixture into a state wherein a solid phase and a liquid phase coexist, whereby all of the (a) element in a metallic state and, where present, the (b) element in a metallic state are precipitated as oxides, and   (B) lowering the partial pressure of oxygen and cooling the mixture thus treated;   wherein the oxide of the (a) element and, where present, the oxide of the (b) element are dispersed in the form of fine particles with a particle size of not more than about 0.1 μm uniformly throughout the matrix from the surface to a core thereof.   
     
     
       2. A process for producing a silver-copper alloy metal oxide composite material, comprising the steps of: (A) raising the partial pressure of oxygen and heating therein a mixture comprising silver, copper, (a) from 0.5 to 25% by weight, in terms of elemental metal, of at least one element selected from the group consisting of Mg, Al, Zr, Ca, Ce, Be, Th, Sr, Ti, Cr, Hf and Si in a metallic and/or oxide state and, optionally, (b) from 0.01 to 5% by weight, in terms of elemental metal of at least one element selected from the group consisting of Bi, Pb, Cd, Zn, Sn, Sb, Mn and iron family metals in a metallic and/or oxide state to thereby bring the mixture into a state where a solid phase and a liquid phase coexist, the amount by weight of said copper being equivalent to that of said silver or less, whereby all of the (a) element in a metallic state and, where present, the (b) element in a metallic state are precipitated as oxides,   (B) lowering the partial pressure of oxygen and cooling the mixture thus treated, and optionally,   (C) heating the mixture thus treated under vacuum or in a reductive or neutral atmosphere, whereby deoxidation of copper oxides formed in step (A) being carried out;   wherein the oxide of the (a) element and, where present, the oxide of the (b) element are dispersed in the form of fine particles with a particle size of not more than about 0.1 μm uniformly throughout the matrix from the surface to a core thereof.   
     
     
       3. The process according to claim 1, wherein the mixture used in step (A) comprises an alloy consisting of silver, the (a) element and, optionally, the (b) element. 
     
     
       4. The process according to claim 2, wherein the mixture used in step (A) comprises an alloy consisting of silver, copper, the (a) element and, optionally, the (b) element. 
     
     
       5. The process according to claim 1, wherein the mixture used in the step (A) comprises a sintered product or a green compact consisting of silver, the (a) element and, optionally, the (b) element. 
     
     
       6. The process according to claim 2, wherein the mixture used in the step (A) comprises a sintered product or a green compact consisting of silver, copper and/or a silver-copper alloy, the (a) element and, optionally, the (b) element.